In the field of after market engine performance enhancement, it is often an object of the enhancement to increase power output of the engine. To increase the power output, an engine must either become more efficient or use more fuel/air mixture more quickly and convert the fuel/air mixture into useful power. Various methods of increasing the fuel/air mixture into an engine are available. These methods can involve reducing restrictions on the air as it directed into, or out of, (or a combination of both) the engine, or pressurizing the air in the intake passageway. Likewise, as more air is directed into the engine, more fuel is also necessary. Typically, to direct more fuel into the engine, the pressure of the fuel supply is increased along with the volume of delivery. There are many ways to accomplish this result. One of these methods is to increase the fuel pressure in the fuel rail (pipe) that feeds the fuel injectors.
Most production car electronic fuel injection systems operate at relatively high fuel pressures, typically in the 30 to 50 psi range. The object of the fuel pressure regulator in such a system is to maintain a specified fuel pressure across the fuel injector so its fuel flow characteristics remain constant for all operational parameters of the engine. A typical fuel pressure regulator has a vacuum reference ported to the top chamber of the regulator, which also contains a spring to counter act the vacuum in the chamber. The reason for the use of the vacuum reference is to maintain adequate fuel flow over a wide range of the I.C. engine intake manifold pressures. This is especially important on engines that utilize a forced induction (turbo or super charged) system regardless of type. When the throttle valve is opened, inlet manifold pressure increases. The rise in manifold pressure causes resistance to fuel flowing from the fuel injector. The reduced fuel flow can result in catastrophic engine failure due to an over lean condition.
On a naturally aspirated engine, the intake manifold pressure range can be from 20" Hg vacuum to 29.92" Hg pressure. On an engine with forced induction, the range is significantly higher. On an engine that uses forced induction, the boost pressure is actually transferred to the top chamber to act in assistance to the aforementioned spring to make the fuel pressure higher than the regulator could using spring compression alone.
To accommodate this tuning aspect of fuel flow management, various sizes of pressure regulators are available. Each of these after market fuel pressure regulators is designed to accommodate particular design parameters and include some adjustability in the form of an adjustment screw which varies compression on the biasing spring in the regulator vacuum chamber. In the situation where the fuel return system is sized to accommodate too large a flow of fuel, the tuning of the regulator with the adjustment screw becomes excessively sensitive and adjustment of fuel pressure is difficult. Conversely, if the fuel return system is sized too small, the fuel pressure remains high for an excessive amount of time and a rich mixture will result upon deceleration.